Multi-joint isometric measurement for the evidence-based assessment of upper limb strength impairment in wheelchair athletes with different health conditions: a preliminary study

The present study presents a novel specific multi-joint isometric test to assess upper limb strength impairment for evidence-based classification in wheelchair sports. Sixteen wheelchair athletes participated in this study and were classified according to their type of physical impairment and health condition as follows: athletes with neurological impairment (ANI, n = 5) and athletes with impaired muscle power (IMP, n = 11). In addition, six non-disabled participants formed a control group (CG, n = 6). All the participants performed the isometric propulsion strength test (IPST), evaluating pushing and pulling actions, and two wheelchair performance tests. Excellent relative intra-session reliability scores were obtained for strength values for the ANI, IMP and CG groups (0.90 < ICC < 0.99) and absolute reproducibility showed acceptable scores of SEM (< 9.52%) for IPST pushing action. The ANI had significantly lower scores in strength and wheelchair performance than the IMP and the CG, while no differences were found between the IMP and the non-disabled participants. In addition, no correlations were found for wheelchair athletes between the isometric upper limb strength measure and wheelchair performance. Our findings suggest that the IPST is a valid test for strength measurement in upper limb impairment wheelchair athletes with different health conditions, which must be used in combination with a performance test to obtain a holistic assessment of this population.


INTRODUCTION
Manual muscle testing has been widely used in classification in Paralympic sports to infer loss of strength by rating muscle resistance at different positions or ranges of movement [1]. However, this measurement is questioned due to the poor reliability as a result of the subjective assessment of muscle strength and the ordinal measures applied, which are also limited in defining their relationship with sporting performance [1][2][3]. For the purpose of inferring loss of muscle strength in Paralympic classification, isometric tests appear to have the most validity as they are (a) less training responsive; (b) instrumented, yielding a ratio-scale measure; (c) comprehensive, assessing all muscle actions of importance; and (d) parsimonious, assessing compound (or multi-joint) actions [2,4]. In this regard, some authors have recently published key recommendations to develop isometric measures, suggesting that the most appropriate method to assess impaired strength in para-athletes should be multijoint and isometric tests performed at specific joint angles that facilitate maximum force production in a standardized and sport-specific position [2]. Previous research suggested that isometric strength measures are valid to produce clusters of athletes with similar levels

Multi-joint isometric measurement for the evidence-based assessment of upper limb strength impairment in wheelchair athletes with different health conditions: a preliminary study
isometric propulsion strength test (IPST) and to identify impaired upper limb muscle strength and its relationship with wheelchair propulsion performance. In a prior session the chief researcher visited the three participant clubs and explained the procedures and aim of the investigation to participants and coaches. Testing was conducted over a single session and was supervised by the research team consisting of experts in evidence-based classification sport science. Participants performed the IPST and two wheelchair performance tests -the wheelchair change of direction ability test (WCODA) and the linear wheelchair sprint test (LWST) -in a randomized order. A rest interval of 5 min was allowed between each test in order to reduce the fatigue effects. Prior to the assessment session, wheelchair athletes participated in two familiarization sessions, in which they performed all the tests, with corrections, after the pertinent explications. The experimental protocol was completed on a synthetic indoor court, and the wheelchair athletes used their specific sports equipment (e.g., gloves, strapping). Two wheelchairs (Quickie All Court, Sunrise Medical, Torrance, California) were used by the control group for testing, with the same strapping system as their counterparts. Before each testing session a standardized warm-up consisting of 5 min of self-paced, low-intensity wheelchair propulsion, dynamic stretching and six 5 m sprints was performed.

Participants
Sixteen wheelchair athletes with different physical impairments and six non-disabled participants were recruited from three regional clubs of wheelchair basketball, wheelchair slalom and paratriathlon and were divided into two sub-groups according to the origin of their eligible impairment. Five athletes with spastic and mixed forms of CP (age = 32 ± 10 years; sitting height = 81 ± 6 cm; body mass: 70 ± 14 kg; body mass index = 32 ± 9 kg/m², training experience = 5.5 ± 3 years) composed the sub-group of athletes with neurological impairment (ANI), which presented as global impairment, including upper limbs, lower limbs and trunk. Participants with medical conditions such amputation (n = 3), incomplete lumbar SCI (n = 4) and spina bifida (n = 4) comprised the impaired muscle power sub-group (IMP) (age = 36 ± 11 years; sitting height = 88 ± 10 cm; body mass = 74 ± 19 kg; body mass index = 28 ± 4 kg/m 2 , training experience = 4.5 ± 3.2 years), with impairment below the injured area (upper limbs not affected).
Non-disabled participants comprised the control group (CG) (age = 30 ± 4 years; sitting height = 84 ± 5 cm; body mass = 68 ± 7 kg; body mass index = 23 ± 2 kg/m²). Wheelchair athletes' coaches and adapted physical education teachers formed the CG to ensure regular handling and manoeuvrability of the wheelchair. All participants signed an informed consent form after being informed about the aims and procedures of the experiment and participated voluntarily. The study was conducted according to the Declaration of Helsinki, and the protocol was fully approved by the ethics committee of the authors' university.
Athletes with neurological impairments resulting in ataxia, hypertonia or athetosis (e.g., CP) tend to present highly affected neuromuscular functions, producing a loss of voluntary motor control that varies considerably depending on the severity and the location of the impairment [9][10][11]. Specifically, the presence of spasticity, weakness and abnormal dynamic activation patterns in those para-athletes produces a global motor dysfunction, and it limits their capability to produce force during movement and motor performance [12], which affects the range of motion [13], the ability to rapidly generate force, and the ability to generate maximum force [14]. Considering the aforementioned literature, it seems pertinent to consider that athletes with CP will present less upper limb strength than healthy subjects, which could cause decreases in wheelchair performance (e.g., change of direction ability), although this relationship is still unknown.
In wheelchair court sports, the key determinants of mobility performance are the ability of the athlete to accelerate, sprint, brake and turn with the wheelchair [15,16], so pushing and pulling actions are the main relevant movements. To ensure that an isometric test is valid, sport-specific and related to performance, the participants' position during the test should be related as much as possible to the propulsion actions [2]. Isometric strength tests using multiple joints have been shown to have a stronger relationship with athletic performance [17][18][19], especially when the most specific positions are used and the muscles contributing to the force production are representative of the activity of interest. Upper limb maximal strength has been correlated with wheelchair propulsion acceleration and top speed in wheelchair rugby [20] and wheelchair racing [5] athletes, respectively. During wheelchair propulsion, wheelchair athletes are required to follow the path of the push rim, being part of a shoulder to hand closed chain [21,22]. Shoulder flexion power has been reported as an essential contributor to manual wheelchair propulsion and starting push phase kinematics has been described with a flexion and adduction shoulder movement from an extended and abducted initial position [22][23][24]. Thus, the most parsimonious and sport-specific approach would be a single test, with each athlete positioned in his/her own wheelchair pushing maximally on the push rim, involving key pushing muscle groups [5].
The present study presents a novel specific isometric test to assess upper limb strength impairment for evidence-based classification in wheelchair sports. The aims of this study were (i) to determine the relative and absolute within-day reliability of a sport-specific isometric strength test to assess upper limb strength impairment for wheelchair athletes, (ii) to assess the capacity of a specific multijoint isometric test to determine upper limb strength impairment in wheelchair athletes with different health conditions and non-disabled participants, and (iii) to establish the strength of association between upper limb isometric strength and wheelchair performance.

Experimental design
A cross-sectional design was used to assess the reliability of the sured that participants understood the test procedure and participants performed two submaximal practice trials. All participants were monitored by the same tester and instructed to gradually build towards maximal force over the first 2 s and to maintain that force for the remaining 3 s, based on previous recommendations [5]. The instantaneous force was displayed in real time to ensure that the tri-  [29]. The SEM was calculated using the following formula: SEM = SD and expressed as a percentage of the mean scores (SEM%) considering values lower than 10% as acceptable [30]. maximal speed." The best score was used for further statistical analysis ( Figure 2B).

Statistical analyses
Data are presented as mean ± standard deviations (SD). The normal distribution of the results of the variables applied was tested using the Kolmogorov-Smirnov test, and statistical parametric techniques were carried out. Relative and absolute reliability among trials in each test was assessed using intra-class correlations (ICCs) and standard  large; 0.7-0.9, very large; and > 0.9, nearly perfect [30]. If the 90% confidence limits (CLs) overlapped small positive and negative values, the magnitude was deemed unclear; otherwise, the magnitude A one-way analysis of variance (ANOVA) with a least significant difference post hoc comparison (Bonferroni correction) was used to examine isometric strength push and pull actions and wheelchair performance mean differences among groups (i.e., ANI, IMP and CG).
Practical significance was assessed by calculating Cohen's effect size (ES) [31]. ES of above 0.8, between 0.8 and 0.5, between 0.5 and 0.2, and lower than 0.2 were considered as large, moderate, small, and trivial, respectively. Paired comparisons among groups for each variable were expressed using mean differences, calculated as: mean  Abbreviations: SD = standard deviation; ES = Effect size; ANI = athletes with neurological impairment; IMP = athletes with impaired muscle power; CG = control group; F peak Push = maximal horizontal peak force in push action; F peak Pull = maximal horizontal peak force in pull action; WCODA = wheelchair change of direction ability test; LWST = linear wheelchair sprint test. * Significant level set at p < 0.05; ** Significant level set at p < 0.01. were related to better performance in the LWST for the non-disabled participants.

Mean ± SD [confidence intervals (95%)] Mean difference (%); ES, interpretation ANI (n = 5) IMP (n = 11) CG (n = 6) ANI-IMP ANI-CG IMP-CG
Although previous studies have shown excellent reproductivity of the isometric upper limb test, assessing F peak in wheelchair athletes [33] and the non-disabled population [7], the feasibility and reliability of those measurements have not been studied for specific Previous researchers agree that test batteries developed for the purposes of evidence-based classification should favour multi-joint actions wherever possible and a sport-specific approach to assess upper limb isometric strength in wheelchair athletes [5,33]. Our results showed that ANI produced less isometric force (F peak ) during all test conditions compared to the IMP and CG participants, being diminished selective motor control [35]. In addition, neural (e.g., motor unit recruitment) and muscular factors (e.g., morphology of muscle fibres) reduce voluntary muscle activation, and consequently a lower muscle force is produced [35,36]. Thus, athletes with physical impairment such as hypertonia could present an inconsistent strength impairment distribution along all of the muscle structures required for optimal wheelchair propulsion, these being the shoulder flexors/adductors, the elbow extensors and wrist pronators [22]. Additionally, was deemed to be the observed magnitude [32]. Data analysis was carried out using IBM SPSS Statistics for Windows, version 25.0 (IBM Corp., Armonk, NY, USA). Statistical significance was set at p < 0.05.

RESULTS
Within-session reliability for each player was evaluated among the three trials performed. Excellent relative intra-session reliability scores were found for F peak values for the ANI, IMP and CG groups  A key step towards evidence-based classification systems in parasport is developing valid tests of impairment and establishing their relationship with sports performance [38]. The results obtained in the current study show unclear correlations between IPST and the two performance tests for both sub-groups with physical impairments, which do not support previous findings. Regarding this, Connick et al. [5] reported that a multi-joint (combining arm push with trunk flexion) strength measure significantly correlated with a 15 m wheelchair propulsion sprint test. These results could be due to the fact that these authors conducted the correlation test using the overall sample.
On the other hand, Mason et al. [33] reported that six upper body isometric strength tests correlated with a 2 m and 10 m sprint, although the sample (i.e., athletes without trunk function) and the used test (i.e., single-joint actions) were different from those in our study.
Additionally, our results show a significant correlation between isometric strength in the push condition and wheelchair sprint in 4 m for the CG participants. An explanation for the above observation is that the type of physical impairment and health condition influences the association between the strength test and wheelchair performance.
These results could be explained by the fact that the strength test might be associated with the level of spasticity that affects athletes with CP and may be collinear with other physical impairments such as motor coordination [39], whereas in athletes with SCI or SB trunk function impairment should be considered [40].
The main limitation of this study was the sample size in regard to the number of players of each group. A larger sample should be analysed, including more wheelchair athletes with a broader range of underlying health conditions leading to upper limb strength impairment. Also, physical activity between tests was not recorded, which could have influenced the obtained results. Likewise, for further investigation, it would be useful to assess the test-retest reliability of the multi-joint upper limb strength measure. To ensure greater reproducibility of the data, focusing a familiarization period could be employed for impaired participants for the IPST to ensure that variability is not a result of the nature of the impairment. Finally, while the isometric test measures have been correlated with wheelchair propulsion performance for the non-disabled participants, only total time was assessed. Other performance variables, such as maximal velocity or acceleration in the first propulsion, could be appropriate to analyse in studying wheelchair sports.

CONCLUSIONS
In summary, the multi-joint isometric upper limb strength test pre-